Merge #698: do not initialize Decimal from float

2692f7f do not initialize Decimal from float (Ferdinando M. Ametrano)

Pull request description:

  this avoid warnings and prefer explicit proper initialization

  See LedgerHQ/app-bitcoin-new#191

ACKs for top commit:
  achow101:
    ACK 2692f7f

Tree-SHA512: deba1b3b654e89f4b61911b45199b782a961abff9e62496a500852dda0f917bf541e6fd58c17baca6289fe708b94ba7e47b95821ba1479cc9cdbdbb4d38128f9

hwilib/devices/ledger_bitcoin/btchip/btchipHelpers.py

@@ -21,8 +21,8 @@
 import re
 
 # from pycoin
-SATOSHI_PER_COIN = decimal.Decimal(1e8)
-COIN_PER_SATOSHI = decimal.Decimal(1)/SATOSHI_PER_COIN
+SATOSHI_PER_COIN = decimal.Decimal(100_000_000)
+COIN_PER_SATOSHI = decimal.Decimal('0.00000001')
 
 def satoshi_to_btc(satoshi_count):
     if satoshi_count == 0: